Apparatus for removing grit and grease from water

ABSTRACT

A grit-and-grease removal system includes a grit channel for degritting water by promoting settling of grit to the bottom of the channel, the grit being removed from the bottom of the channel by a traveling bridge-type grit removal device supporting a submerged grit pump. The system further includes an elongate grease channel arranged to receive degritted water from the grit channel, and having a plurality of grease skimmer pipes extending across the channel above the water level. The grease skimmer pipes are spaced apart along the length of the grease channel, and each grease skimmer pipe includes a plurality of fluid discharge orifices or nozzles spaced along the length of the pipe and oriented to blow fluid obliquely onto the water surface in the direction of a discharge end of the grease channel so as to move grease floating on the surface to the discharge end. Grease that collects at the discharge end of the grease channel is removed by a conveyor that extends into the water and lifts grease upward and out of the channel.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.09/698,928 filed Oct. 27, 2000, now U.S. Pat. No. 6,551,516, which is acontinuation-in-part of U.S. patent application Ser. No. 09/428,185filed Oct. 27, 1999, now abandoned.

FIELD OF THE INVENTION

The invention relates to water treatment and, more particularly, tomethods and apparatus for removing grit and grease from water.

BACKGROUND OF THE INVENTION

City sewage, industrial waste water, and other types of water frequentlyinclude relatively large concentrations of both grit and grease. Thetreatment of waste water to remove impurities is generally performedwith the aid of treatment devices whose operation and/or reliability canbe adversely affected by grit and grease. Grit can be highly abrasive onpumps and the like, can clog filters and conduits, and can build up intanks and thereby reduce the effective tank volume. Furthermore, excessgrit can make handling and dewatering of sludge more difficult. Greasecan form deposits on machinery to the point of interfering with properoperation of the machinery. Grease can also encourage the growth ofmicrobes. Thus, it is common practice to subject waste water to aninitial pretreatment operation to remove grit and grease prior tofurther treatment of the water to remove other impurities.

Grit is often removed by a process of sedimentation wherein water to betreated is introduced into a settling tank or the like and is allowed toremain long enough to permit grit, which is generally of greaterspecific gravity than water, to settle to the bottom of the tank. Whilein the settling tank, the water may be subjected to processes such asaeration designed to promote more-rapid settling of the grit, andadditionally may be circulated or perturbed in such a way as toencourage grit to settle preferentially in certain regions of the tank.The grit is then removed from the bottom of the tank by any of varioustypes of devices including scrapers, conveyors, pumps, and the like. Onetype of grit removal device that has been used in elongate grit settlingchannels is a traveling bridge-type device that travels lengthwiseback-and-forth along the grit settling channel. The travelingbridge-type device supports a device that extends to the bottom of thechannel and removes grit upwardly through a conduit and discharges thegrit outside the grit channel.

A combined grit-and-grease removal system that has been developed by theassignee of the present application employs a grit channel and travelingbridge-type grit removal device as described above, in combination witha grease channel that receives degritted water from the grit channel andprocesses the water to remove grease. More specifically, grease isremoved from the surface of the water in the grease channel by a skimmerassembly that is connected with the traveling bridge-type grit removaldevice so as to travel back-and-forth along the length of the greasechannel, which extends parallel to the grit channel. The skimmerassembly collects grease that is floating on the surface, and a greasehoist assembly removes grease from the skimmer and carries it upwardlyand out of the grease channel, where it is deposited into a greasebucket. The grit-and-grease removal system having the traveling skimmerassembly can be used only in installations in which the grease channelaffords an unimpeded path for the passage of the skimmer. Furthermore,the traveling skimmer works only intermittently when the travelingbridge makes an excursion along the channels.

SUMMARY OF THE INVENTION

Accordingly, it would be desirable to provide a grit-and-grease removalsystem having improved grease removal components that would not limitthe application of the system to installations providing an unimpededpath along the length of a grease channel. It would also be desirable toprovide a grit-and-grease removal system capable of providing continuousgrease removal.

The above needs are met and other advantages are achieved by the presentinvention, which provides a system for removing grit and grease fromwater in which grease removal is effected without the use of any skimmerassembly that travels the length of the grease channel, and in whichgrease removal can be carried out continuously.

In accordance with a preferred embodiment of the invention, agrit-and-grease removal system includes an elongate grit channelconfigured to receive water from a source, a traveling grit removaldevice operable to traverse a length of the grit channel and remove gritsettled on the bottom of the grit channel, an elongate grease channelarranged to receive degritted water from the grit channel, and aplurality of grease skimmers positioned in the grease channel so as tobe above an upper surface of water contained in the grease channel. Thegrease skimmers are spaced apart along a length of the grease channeland are adapted to receive fluid from a source, each grease skimmerhaving fluid discharge orifices oriented to direct fluid obliquely ontothe surface of the water in a direction toward a discharge end of thegrease channel so as to move grease floating on the surface toward thedischarge end. The system also includes a grease removal device locatedat the discharge end of the grease channel and operable to remove greasefrom the water surface and deposit the removed grease outside the greasechannel.

The system is thus amenable to installations in which it would bedifficult to employ a traveling grease skimmer because of structureimpeding the free passage of a skimmer. Additionally, in the priorgrit-and-grease removal system employing the traveling grease skimmer,it was generally necessary to place the grease channel immediatelyadjacent and parallel to the grit channel and to have the length of thegrease channel coextensive with that of the grit channel so that whenthe traveling grit removal device was traversed along the grit channel,the grease skimmer was also traversed along the grease channel. In thepresent invention employing non-traveling grease skimmers for greaseremoval, it is no longer necessary to make the grease channelcoextensive with the grit channel, although it may still be advantageousto do so for other reasons. The system of the present invention alsoenables continuous grease removal, and does so at a relatively lowcapital cost inasmuch as grease skimmer devices can be made relativelyinexpensively.

In a further preferred embodiment of the invention, the grit channelalso includes aeration devices disposed in the grit channel so as to besubmerged in water contained therein. The aeration devices are adaptedto receive air from an air supply and to release air into the wastewater. A first set of aeration devices impart motion to the grit/watermixture in the “dead zone” adjacent the front wall of the grit channelwhere the water to be treated flows into the channel, so as to preventgrit from immediately settling out and accumulating against the frontwall. Farther down the grit channel, additional aeration devices promotesettling of grit to the bottom of the channel. Preferably, the fluidused by the grease skimmers comprises air, and the grease skimmers andthe aeration devices are supplied with air from a single common airsupply. Thus, in installations employing aeration for grit removal, itis relatively simple and inexpensive to incorporate grease removal inaccordance with the present invention since air for the grease skimmersis already available from the air supply used for the aeration devices.

Alternatively, the grease skimmers can employ fluids other than air,including other gases, or liquids such as water. For example, water canbe pumped from one of the channels (preferably from the grease channel)and supplied to the grease skimmers.

The grease skimmers advantageously can be formed by a plurality of pipesextending transversely across the grease channel and spaced apart alongits length. Each pipe preferably includes a plurality of spaced-apartorifices or nozzles formed through its side wall for discharging fluidonto the surface of the water. By appropriate location of the orifices,fluid can be impinged onto the water surface across substantially theentire width of the grease channel.

The grease removal device for removing grease from the water surface atthe discharge end of the grease channel preferably comprises an inclinedconveyor that lifts grease upward and away from the grease channel andallows any water also removed by the conveyor to continually flow backdown the conveyor into the grease channel. Thus, the conveyor preferablyperforms a dewatering operation on the removed grease. Suitableconveyors include continuous belt conveyors and screw-type conveyors.The grease skimmers in concert with the conveyor enable grease to beremoved on a continuous basis, independent of the operation of thetraveling grit removal device.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features, and advantages of the inventionwill become more apparent from the following description of certainpreferred embodiments thereof, when taken in conjunction with theaccompanying drawings in which:

FIG. 1 is a top elevation of a grit-and-grease removal system inaccordance with a preferred embodiment of the invention, in which air isthe fluid used by the grease skimmers;

FIG. 2 is a somewhat enlarged top elevation of a portion of the systemof FIG. 1;

FIG. 3 is a further enlarged sectioned end elevation of one of thegrease skimmers of the system in FIG. 1;

FIG. 4 is a cross-sectional view taken on line 4—4 of FIG. 1;

FIG. 5 is a cross-sectional view taken on line 5—5 of FIG. 1; and

FIG. 6 is a cross-sectional view similar to FIG. 4, showing analternative embodiment in which water is the fluid used by the greaseskimmers.

DETAILED DESCRIPTION OF THE DRAWINGS

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Likenumbers refer to like elements throughout.

With reference to FIGS. 1-4, a grit-and-grease removal system inaccordance with a preferred embodiment of the invention is broadlydesignated by reference numeral 10. The system 10 includes an elongategrit channel 12 defined by a pair of spaced-apart longitudinal walls 14and 16 that are oriented generally vertically and project upwardly froma bottom wall 18, and opposite end walls 20 and 22 connected between theends of the longitudinal walls and projecting upwardly from the bottomwall 18. The system also includes an elongate grease channel 24 definedby the longitudinal wall 16 and a second longitudinal wall 26 spacedtherefrom, and by opposite end walls 28 and 30 connected between theends of the longitudinal walls 16 and 26, the walls 26, 28, and 30projecting upwardly from a bottom wall 32 which, advantageously, can beformed integral with the bottom wall 18 of the grit channel 12. Thus,the longitudinal wall 16 is a common wall separating the grit channel 12from the grease channel 24. The wall 16 preferably includes aperturesand/or baffles operable to pass degritted water from the grit channel 12into the grease channel 24. The design of suitable apertures and bafflesfor passing the water is within the capabilities of one of ordinaryskill in the art, and hence the apertures and/or baffles are not furtherdescribed herein.

Water to be treated flows into one end of the grit channel 12 through anin-feed channel or conduit 34. Grit contained in the water settles tothe bottom wall 18 of the grit channel. In some cases, there can be atendency for grit to immediately settle to the bottom of the gritchannel 12 adjacent to the front end wall 20, and to accumulate againstthe front end wall. This area is referred to as the “dead zone” becausethe flow velocities in this region tend to be low and recirculationtends to occur. It is undesirable to have large accumulations of grit inthis area. Accordingly, in accordance with a preferred embodiment of theinvention, the system 10 advantageously includes a “dead zone diffusersystem” 31, as best seen in FIG. 5. The dead zone diffuser system 31includes a mid-depth orifice bar 33 and a full-depth orifice bar 35,each defining a plurality of orifices for discharging air jets into thewater. Each of the orifice bars may be formed by a pipe having a seriesof orifices through its side wall and being capped at both ends. Forinstance, a one-inch diameter PVC pipe having {fraction (1/16)}-inchdiameter holes drilled through one side can be used. The orifice barscan be connected to a generally vertical air supply pipe 37 that issubmerged in the water and in turn is connected to a main air supplypipe 38 that extends along the length of the grit channel 12 adjacentthe longitudinal wall 14. The mid-depth orifice bar 33 is positioned atabout half the depth of the water in the grit channel, for example about3 feet above the bottom wall of the channel. The full-depth orifice bar35 is positioned near the bottom wall of the channel, for example about6 inches above the bottom wall. The air jets discharged by the orificebars impart motion to the grit/water mixture, thereby helping to keepthe grit in suspension so that it does not immediately settle out andaccumulate against the front end wall 20.

The grit channel 12 also includes a plurality of aerating devices 36 forreleasing air into the water contained in the channel so as to promotesettling of grit farther down the channel from the dead zone. Theaerating devices 36 advantageously comprise a series of coarse bubblediffusers distributed along the length of the channel so as to besubmerged in the water. Air is supplied at a sufficient pressure,usually empirically determined at the site, to the bubble diffusers bythe main air supply pipe 38, and a series of feeder pipes 39 (one shownin FIG. 4) that branch off the main air supply pipe 38 and feed theindividual bubble diffusers. The aerating devices 36 advantageously areoperable to create a spiral circulation of water in the grit channel,which causes grit to be scoured from the bottom of the channel into arecessed portion 41 (FIG. 4) of the bottom wall 18. The spiralcirculation velocity caused by the aerating devices 36 determines thesize and specific gravity of grit removed in the grit channel 12. Thus,the quality and particle size of the removed grit can be selectivelyvaried by varying the air pressure supplied to the aerating devices 36,thereby varying the spiral circulation velocity in the grit channel.

Grit that has settled to the bottom of the grit channel 12 is removed bya traveling grit removal device 40 that is operable to travel along thelength of the channel in a back-and-forth motion. The traveling gritremoval device 40 includes a bridge 42 that spans the grit channel 12,extending transversely between the longitudinal walls 14 and 16. Thebridge 42 includes wheels 44 (best seen in FIG. 4) that engage upperedge portions of the walls 14 and 16 and operate to allow the bridge 42to roll along the grit channel. A drive device (not shown) is coupledwith the bridge 42 for causing movement of the bridge along the channel.The drive device can comprise a motor coupled with one of more of thewheels 44 for rotatably driving the wheel or wheels. However, othertypes of drive devices alternatively can be used. The bridge 42 supportsa conduit 46 that extends generally vertically downward from the bridgeto a lower end of the conduit disposed proximate the bottom wall 18 ofthe grit channel. In one embodiment of the invention, a submerged pump(not shown) is supported by a conduit support structure (not shown) thatextends along the conduit 46, such that the pump is proximate the bottomwall 18 of the channel. The pump is operable to suction grit and waterthrough an intake structure of the pump located adjacent the bottom wall18, and to pump the suctioned grit and water upwardly through theconduit 46 to an upper end of the conduit 46 located on the bridge 42.The upper end of the conduit 46 is connected by a flexible hose 54 to ahorizontally extending discharge conduit 56 that extends from the bridge42 to a grit discharge trough that is further described below. Thedischarge conduit 56 is supported by the bridge 42 such that it travelsback-and-forth along with the bridge. A pump mounted on the bridge 42can be used instead of a submerged pump for pumping grit and water upthrough the conduit 46. In other embodiments of the invention, thesubmerged pump can be eliminated and a scraper device supported by thetraveling bridge 42 can be used to scrape grit on the bottom wall 18 toa location where it can be suctioned or otherwise removed from the gritchannel 12.

A discharge end of the discharge conduit 56 is positioned to dischargegrit and water into a grit discharge trough 58 that advantageouslyextends parallel to the grease channel 24 on an opposite side thereoffrom the grit channel. The grit discharge trough 58 can be formedintegrally with the longitudinal wall 26 of the grease channel, oralternatively can be formed separately from the grease channel. Adischarge end of the trough 58 feeds grit and water mixture into a gritclassifier 60 operable to separate grit from the water. Grit isdeposited by the classifier 60 into a grit container 62, and water fromwhich a majority of the grit has been removed is returned to the in-feedchannel or conduit 34 via a conduit 64. The grit classifier 60advantageously comprises a screw conveyor-type classifier.

As previously noted, water that has been degritted in the grit channel12 is passed from the grit channel into the grease channel 24. Greasecontained in the water in the grease channel 24 tends to rise to thesurface of the water and float thereon. The grit-and-grease removalsystem 10 includes devices for removing the grease from the watersurface. More particularly, the system 10 includes a plurality of greaseskimmers 66 that extend transversely across the grease channel 24 andare positioned above the surface of the water. As best seen in FIGS. 2and 3, each grease skimmer 66 includes at least one fluid dischargeorifice or nozzle 68 oriented to blow fluid obliquely onto the watersurface in a direction toward a discharge end of the grease channel.More preferably, each grease skimmer 66 includes a plurality of orificesor nozzles 68 spaced apart across the width of the grease channel 24such that fluid is blown onto the water surface across substantially theentire width of the channel. The fluid blown onto the water surfacetends to move grease floating on the water toward the discharge end ofthe channel. The grease skimmers 66 advantageously are spaced apartalong the length of the grease channel 24 with a spacing sufficientlysmall to enable each skimmer 66 to move grease at least as far as thenext adjacent skimmer, such that grease is passed from one skimmer tothe next, and so on, until the grease is moved to the discharge end ofthe channel.

The grease skimmers 66 are supplied with fluid by a fluid supply pipe 70and a fluid distribution pipe 72 connected to the supply pipe 70. Thefluid distribution pipe 72 preferably extends along the length of thegrease channel 24 adjacent one wall thereof. The grease skimmers 66branch off the distribution pipe 72 at a plurality of points along itslength. Preferably, the grease skimmers 66 comprise pipes havingorifices or nozzles 68 formed through their side walls. Where the fluidused for the grease skimmers comprises air, the supply pipe 70 for thegrease skimmer system preferably is connected to the air supply pipe 38for the grit channel aeration system, whereby both the aeration systemand grease skimmer system can be supplied by a single common air supply74 as shown in FIG. 1.

An alternative embodiment of the invention depicted in FIG. 6 employswater rather than air as the skimming fluid for the grease skimmers 66.To this end, a water supply pipe 70′ preferably extends down into thegrease channel and is connected at its lower end to a submerged waterpump 71 located in the grease channel. The pump 71 pumps water from thegrease channel up through the water supply pipe 70′, which is connectedto the fluid distribution pipe 72. Alternatively, of course, the pump 71could be located outside the grease channel. Thus, water is supplied tothe grease skimmers 66 from the distribution pipe 72. The greaseskimmers discharge the water obliquely onto the surface of the water inthe grease channel so as to move grease toward the discharge end of thechannel.

Grease that has been moved to the discharge end of the grease channel 24is removed from the water surface by a conveyor 76 positioned at thedischarge end. The conveyor 76 can comprise any device capable ofremoving grease from the water surface and transporting the greaseoutside the grease channel. For example, the conveyor 76 advantageouslycan be a continuous belt conveyor positioned such that a portion of thebelt extends into the water, with the belt being inclined and driven tocarry grease upward and out from the channel. Alternatively, theconveyor 76 can be an inclined Archimedes screw-type cylindricalconveyor having a lower end extending into the water and an oppositeupper end positioned outside the grease channel 24. A conveyor shouldprovide for flow of water back into the grease channel as the grease isremoved, since any grease removal device inevitably will also removesome amount of water along with the grease. One way in which this can beaccomplished is to use a shafted screw-type conveyor. Another way inwhich this can be accomplished is to provide screw flights in theabsence of a central shaft. The flights pick up and transfer the greasewhile water returns to the channel for separate discharge through thecentral axis about which the flights rotate. Thus, the conveyor dewaterthe grease removed from the grease channel. Grease can be removed fromthe conveyor 76 by a scraper device or the like (not shown) at an end ofthe conveyor remote from the grease channel, and the removed grease canbe deposited into a suitable container or into a conduit for carryingthe grease to a further processing device.

The conveyor 76 can be positioned to extend transversely from thelongitudinal wall 26 of the grease channel 24 as shown in FIG. 1. Inthis case, the conveyor 76 preferably extends through a bore or cutoutformed in the wall 26 above the water level but below the level at whichthe grit discharge trough 58 is mounted, and the conveyor 76 extendsbeneath the grit discharge trough 58 as shown in FIG. 1. Alternatively,the conveyor 76 can be positioned to extend longitudinally from the endwall 28 of the grease channel.

Many modifications and other embodiments of the invention will come tomind to one skilled in the art to which this invention pertains havingthe benefit of the teachings presented in the foregoing descriptions andthe associated drawings. Therefore, it is to be understood that theinvention is not to be limited to the specific embodiments disclosed andthat modifications and other embodiments are intended to be includedwithin the scope of the appended claims. Although specific terms areemployed herein, they are used in a generic and descriptive sense onlyand not for purposes of limitation.

What is claimed is:
 1. A system for removing grit and grease from wastewater, comprising: an elongate grit channel configured to receive wastewater from a source and operable to allow grit to settle to a bottom ofthe grit channel; a traveling grit removal device operable to traverse alength of the grit channel and remove grit from the bottom of the gritchannel; an elongate grease channel arranged to receive degritted waterfrom the grit channel; a plurality of grease skimmers positioned in thegrease channel so as to be above an upper surface of water contained inthe grease channel, the grease skimmers being spaced apart along alength of the grease channel and adapted to receive fluid from a source,each grease skimmer having fluid discharge orifices oriented to directfluid obliquely onto the surface of the water in a direction toward adischarge end of the grease channel so as to move grease floating on thesurface toward the discharge end; and a grease removal device located atthe discharge end of the grease channel and operable to remove greasefrom the water surface and deposit the removed grease outside the greasechannel, wherein the grease removal device comprises a conveyor operableto lift grease from the water surface and transport the grease upwardlyand outwardly away from the grease channel while causing water removedalong with the grease to flow back down the conveyor into the greasechannel.
 2. The system of claim 1, further comprising aeration devicesdisposed in the grit channel so as to be submerged in waste watercontained therein, the aeration devices being adapted to receive airfrom an air supply and to release air into the waste water.
 3. Thesystem of claim 2, wherein the fluid discharged by the grease skimmerscomprises air and the aeration devices and the grease skimmers areconnected so as to be supplied with air from a single common air supply.4. The system of claim 2, wherein the aeration devices include air-jetdevices disposed adjacent an in-flow end of the grit channel where waterto be treated flows into the grit channel, the air-jet devices beingoperable to discharge air jets into the water to impart motion to thewater so as to discourage grit from immediately settling to the bottomof the grit channel adjacent the in-flow end.
 5. The system of claim 4,wherein the air-jet devices include a first air-jet device positionedproximate the bottom of the grit channel and a second air-jet devicespaced above the first air-jet device.
 6. The system of claim 1, whereinthe grit and grease channels extend parallel to one another and areseparated by a common wall that is operable to pass degritted water fromthe grit channel into the grease channel.
 7. The system of claim 6,wherein the grit channel includes an additional wall extending parallelto and spaced from the common wall, upper portions of the walls of thegrit channel defining a track along which the traveling grit removaldevice travels.
 8. The system of claim 1, wherein the grease skimmerscomprise pipes extending transversely across the grease channel andhaving orifices formed through a side wall of each pipe for dischargingfluid therefrom.
 9. The system of claim 8, wherein each grease skimmerpipe includes a plurality of orifices spaced lengthwise along the pipe.10. The system of claim 1, further comprising a grit discharge trough,the grit removal device being arranged to discharge grit into the gritdischarge trough.
 11. The system of claim 10, further comprising a gritclassifier arranged to receive a mixture of grit and water from the gritdischarge trough and operable to separate the grit from the water.